Endoscopy significantly improves the diagnosis of tumors of the stomach; however, its value may be limited in differentiating benign from malignant gastric ulcers (MGUs). The accuracy of endoscopy was compared in 20 patients with MGU studied by endoscopy, biopsy, and cytology. Endoscopy correctly diagnosed 13 cases (65%), with endoscopic signs being benign or indeterminate in the remaining seven. However, all 20 MGUs were accurately diagnosed since biopsy and cytology increased the diagnostic accuracy of endoscopy in the remaining seven patients. The combination of biopsy and cytology yielded a positive diagnosis in 19 patients (95%); the remaining patient was operated on with only the endoscopic diagnosis of MGU. The complementarity of these three techniques was highlighted in five cases where only one of the procedures unequivocally diagnosed malignancy. It is concluded that biopsy and cytology are useful complementary techniques and should always be performed together in categorizing the nature of all gastric ulcers despite a benign macroscopic appearance at endoscopy.